Perl does an internal magic error correction/guessing when printing a number like 195.999999...etc to compensate rounding errors on the last digits. (This of course in binary and not decimal representation)

I think that's why it prints $x1 as 196.

I'll check as soon my laptop is up and running.

update

as I thought, it's compensating the rounding error from not being able to accurately represent 0.15 in a based 2 floating number:

  DB<28> $x1 = (1.15*170)+0.50;

  DB<29> printf("%.20f",$x1)
195.99999999999997000000
  DB<30> printf("%.20f",0.15)
0.14999999999999999000
  DB<31>
[download]

There is an easy workaround , avoid the decimal point when calculating and divide at the very end.

  DB<35> $x1 = (115*170)+50; # no fractions

  DB<36> $x1 /=100

  DB<37> p "$x1 = ",int $x1
196 = 196
  DB<38>
[download]

see also Humans have too many fingers